Kate Upton hit a milestone on June 10: The hot Sports Illustrated swimsuit model, who is known for her impressive cleavage, turned 21 years old.

Despite her youth, the buxom beauty has seen her career blossom from a no-name Victoria's Secret catalogue girl to one of the most famous faces of the decade. (Take that Gisele Bundchen and Kate Moss!)

It was Upton's barely-there bikini on the cover of the 2012 Sports Illustrated swimsuit edition which sparked interest in the young model but her second cover in 2013, which showed the busty blond in a bikini bottom, winter parka and her massive cleavage, cemented Kate's status as a girl to watch. (And watch they did. Kate's infamous "Cat Daddy" video now has almost 17 million views on YouTube.)

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From there, the fashion elite came a knockin'. From an animal centric high fashion shoot in Harper's Bazaar to her very first US Vogue cover, the leggy model has been rising up the fashion ranks.

So, in honour of the birthday girl, we present to you the hottest photos of Kate Upton.

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